This invention relates to a vehicle speed control device which maintains a desired constant traveling speed of a vehicle.
One example of a conventional vehicle speed control device for maintaining a constant speed of a vehicle is shown in FIG. 5.
As shown in FIG. 5, an ignition switch 31 has one terminal connected to a power supply, such as a battery (not shown) and another terminal to a main switch circuit 33 which is in turn connected to a speed control means, such as a CPU (central processing unit) 35. The main switch 33 includes a self-return type main switch 32 which is installed inside the vehicle near the operator of the vehicle and activated by the operator for constant speed travelling, and a relay switch 34 which is turned on or closed when the main switch 32 is turned on. Therefore, when the ignition switch 31 and the relay switch 34 are turned on, an operation power is supplied from the power supply to the CPU 35, so that the CPU 35 becomes energized for performing an operation for constant speed traveling.
The main switch circuit 33 further includes a normally closed-type release switch 36, and a relay coil 37 which turns on the relay switch 34 when the relay coil 37 is energized. A series circuit connecting the main switch 32, the release switch 36 and the relay coil 37 in series has one end connected to a connecting point S of the ignition switch 31 and the relay switch 34, and another end to a common ground. A connecting point T of the main switch 32 and the release switch 36 is electrically connected to a connecting point U of the relay switch 34 and the CPU 35, thus forming a self-hold circuit. Therefore, even when the main switch 32 is turned off or open, the relay switch 34 remains turned-on until the release switch 36 is activated.
A control switch 38 is adapted to set and reset a speed of constant speed traveling by the operator of the vehicle and generates an instruction signal representing the speed. The CPU 35 then generates in response to the instruction signal a drive control signal to an actuator 39. The actuator 39 then controls the extent of opening of a throttle valve 40 which in turn controls the amount of air sucked into an engine in response to the control signal. For example, if a "set" switch in the control switch 38 is activated when the traveling speed of the vehicle is 40 km/h, the CPU 35 stores that speed in memory and effectuates the actuator 39 to maintain that speed for the vehicle even if an acceleration pedal is not applied.
However, in the conventional vehicle speed control device, the constant speed traveling becomes effectuated even during the time immediately after the ignition switch 31 is turned on. Therefore, the conventional control device is disadvantageous because the output of the engine is not stable immediately after the start of the engine, the constant speed traveling is not properly carried out.